This is can important factor to consider when planning treatment. If lengthening is carried out in a condition which is progressive e.g. Ollier's diseases, a repeat lengthening would be required at skeletal maturity. On the other hand, posttraumatic malunions may give rise to a static limb length discrepancy.

Shapiro has studied the growth patterns in lower extremity length discrepancies and classified them into 5 patterns. Important in this is type 1 or an upward slope pattern in which the length discrepancy increases with time at the same proportional rate. This happens for example in the proximal focal femoral deficiencies in Ollier's disease and with physeal damage.

Other patterns show varying response with time, e.g. Type V which shows a gradual reversal of the limb discrepancy with time. This underlines the importance of a repeated and regular evaluation and charting of the discrepancy to enable conclusions to be formed about the projected final limb length discrepancy.

The clinical examination

A thorough clinical examination is a must and this would demand a degree of expertise in evaluating the true lower limb lengths, in evaluating the role of other concomitant deformities like flexion/abduction deformity at the hip or pelvic obliquity due to other causes.

True lower limb lengths are obtained by squaring the pelvis if possible and keeping the lower limbs in identical position. Measurement of the length is taken from the anterior superior iliac spine to the knee joint line and the second from the knee to the medial malleolus indicating the tibial length.

Apparent limb lengths are measured by keeping both lower limbs parallel to each other and in the long axis of the body. It does not take any note of the position of the pelvis which will be not be square if there are hip deformities of abduction or adduction or suprapelvic contractures giving a pelvic obliquity. If these deformities are not all correctable or not to be corrected, the apparent limb length will form the basis for all calculations of the discrepancy.

In the clinical examination, it would be important to assess the status of all joints for presence of deformity, the joint range of motion & stability, the local neurovascular status and the gait of the patient. A thorough general examination is mandatory. Wooden blocks are used to level the pelvis on standing to assess the discrepancy and the raise, which may be required. An easy method of knowing what the patient will be like functionally after lengthening - temporary shoe lifts can be given and the patient assessed.

When considering enhancement of stature, it is important to measure the ratio of the upper segment to that of the lower segment, the sitting height and subischial limb length as well as the upper limb lengths and their level relative to the lower limbs on standing.

Radiographic measurement of limb length discrepancy:

Because clinical measurement of limb lengths has some fallacies and inter-observer errors, x-rays are utilized for limb length measurements. Two commonly employed methods of x - ray measurement are the teleoroentgenogram and the scanogram. Both techniques use a radio-opaque ruler kept alongside the extremity during the exposure.

The teleoroentgenogram is used for small children below the age of 5 to 6 years. In this a single exposure is made from the hip to the ankles and the length read on the ruler markings. The scanogram is used for larger children and it utilizes sequential exposures of the hips, knees and ankles and reads their level on the ruler. This technique requires that the child be still so that lower limb position in relation to the ruler is not altered during different exposures. These techniques provide a reliable method of storing data for future reference and for calculating the final growth discrepancy.

Limb lengths can also be measured utilizing CT scans but at present this is costly. Ultrasound has also been employed for this but is subject to inter-observer errors.

Projection of limb length discrepancy

It is important to know what the final discrepancy of limb length at skeletal maturity will be. A rough idea can be gained by repeated measurements and calculation of the percentage inhibition in relation to the normal limb. The growth of the normal limb in terms of percentile is charted and on this basis the length of the normal limb at maturity is calculated. Applying the percentage inhibition the length of the affected limb can be calculated.

There are a number of fallacies involved in these methods. Firstly growth does not proceed in a linear fashion. It is age dependent and in the case of the affected lower limb it is dependent on the etiology of limb shortening. Secondly, normal limb length data is not available for Indian population. The available charts are those of Green - Anderson growth prediction chart and the Moseley straight line graph. Thirdly, the skeletal age according to the Greulich and Pyle's atlas itself is an approximation.

Menelaus predicts growth by a simple method of calculating growth of the distal femur at 3/8 inch per year and that of the proximal tibia at 1/4 inch per year in adolescents over 9 years of old age. Growth ceases at age 14 years in girls and in age 16 years in boys.